1. Field of the Invention
This invention relates generally to the fabrication of magnetic read and write-heads and more particularly to a method of manufacture that eliminates or significantly reduces the occurrence of electrostatic discharge damage to a GMR read-head during the fabrication process.
2. Description of the Related Art
A magnetic data recording hard disk drive employs a plurality of slider-mounted electromagnetic transducers, a typical one of the prior art being schematically shown in FIG. 1. In a state-of-the-art disk drive, each transducer (1), which is formed on a slider substrate (20) (typically formed of AlTiC) further includes of a read-head (2) and a write-head (4). The combined read head, write head and an additional encapsulating and overcoating layer (12), which are together called the slider-mounted transducer, are produced in great quantities of identical units on a substantially circular wafer (see FIG. 2b). The wafer is then sliced into rows (called row-bars) along chords of the circular wafer and subsequently processed and formed into more complicated assemblies as will be discussed below.
The read-head (2) is typically a multi-layered sensor whose operation is based on the giant magnetoresistive (GMR) effect and, because of the extreme thinness of its magnetic layers, it is extremely sensitive to electrostatic discharge (ESD). The write-head is typically an inductive coil (coil cross-sections shown as (6)) wrapped around a magnetic core (18), which is fairly immune to ESD. The read-head is typically protected from stray electromagnetic fields during disk drive operation by an upper shield (8) and an under-shield (10). A dielectric layer (11), typically alumina, insulates the under-shield from the GMR sensor (13) and an identical layer (also shown as (11)) also insulates the GMR element from the upper shield (8). The shields, dielectric layers, GMR read-head and encapsulating/protective overcoats are sequentially formed on a substrate (20), which, when properly cut, will form the slider-mounted transducer (discussed below). The combined read/write-head (transducer) is typically encapsulated in an insulating alumina deposit (12) and conducting leads (not shown) from the GMR element and the write head coils pass through the encapsulation and are connected to conducting pad-shaped terminals (usually gold or similar highly conducting material) (14) on the trailing edge surface (15). The term “trailing” here refers to the position of the edge relative to the direction of disk motion. External circuitry is ultimately connected to these terminals and used to energize the magnetic field of the write head, provide sensing current to the read head and extract a signal from the read-head. Typically (as will be shown in FIG. 2a), there are a set of two terminals for the read head, a set of two terminals for the write head and additional terminals for making connections through the alumina to the substrate (20) and to the shields ((10) and (8)).
The write head's coil-wrapped (6) magnetic core (18) and the read head's GMR sensor element (13), surrounded by insulating layers (11) and upper (8) and lower (10) shields, emerge at the surface of the encapsulating alumina deposit (12). This surface is co-planar with the surface of the slider (22) and is called the air-bearing surface (ABS) because it literally flies over the surface of a disk suspended on a layer of air (or other gases). The surface of the slider and transducer portion is commonly protected by a highly wear-resistant carbon overcoat (21), which is lapped to provide a smooth surface. Each slider and its mounted transducer is mounted on a stainless steel suspension (100), the combination forming what is called a head-gimbals assembly (HGA).
During its operation, as noted above, the slider surface literally flies over the surface of a rapidly rotating disk. The rapidly rotating disk is prone to accumulate static charges which, in turn, can discharge to the slider and damage the sensor within it. Numerous workers in the field have attempted to address the problem of static discharge during sensor operation. The present invention, however, is concerned with protecting the sensor from the hazards of electrostatic discharge during the many manufacturing processes leading up to the fabrication of the head-gimbals assembly.
There are many steps during the assembly process where static charges may build up to sufficiently significant levels that discharge becomes a problem. At the wafer fabrication level, there are a host of vacuum processes, including ion-beam depositions, plasma etches, etc., where charges can build up on exposed surfaces. The wafer must be sliced to create individual transducers and sliders, which also creates static charges. The ABS of the slider must be lapped, also creating static charge accumulations.
Bajorek et al. (U.S. Pat. No. 5,465,186) teaches a method for shunting discharge current away from the read head by soldering the GMR sensor lead terminals together at the slider surface, thereby diverting transient currents during discharge events.
Hughbanks et al. (U.S. Pat. No. 5,491,605) teaches shunting the leads of the read and write head together and connecting them to the slider substrate through a conducting layer, such as tungsten, formed at the ABS.
Erpelding et al. (U.S. Pat. No. 5,699,212) places solder shunts across adjacent leads of the read head.
Girard et al. (U.S. Pat. No. 6,631,052) provides a generalized conductive pathway on which ESD susceptible components are formed. Selected regions of the pathway can then be removed by ablation.
Lam et al. (U.S. Pat. No. 6,704,173) provide a sensor coupled to a suspension assembly through a conducting strip and diode.
Bougtaghou et al. (U.S. Pat. No. 6,643,106) teaches the formation of a shunt made of solder.
Zak (U.S. Pat. No. 5,021,907) teaches a method of discharging accumulated electrostatic charge from a slider during disk drive operation using a gimbal spring apparatus that positions electrical contacts against the slider.
Zarouri et al. (U.S. Pat. No. 6,034,851) discloses a hinged shorting bar and a test clip that can be made to short pads on a connector to a magnetic transducer.
The inventions cited above all require rather significant modifications of the tools, the processes or the sensors themselves, which can potentially increase costs and render the fabrication process less efficient. For example, the removal of extra shorting leads or solder connections or clips can itself create ESD events or damage a sensor.
The present invention proposes a significant improvement over the methods of the prior art, by the use of an easily applied and easily removed conducting adhesive as a mechanism for shorting the read head leads together.